INDIVIDUAL-DIFFERENCES IN SCHEDULE-INDUCED AND CONDITIONED BEHAVIORS

Previous experiments have shown that subjects which exhibit a high loc omotor response to novelty (HR) also show a greater locomotor response to psychomotor stimulants than subjects which have a low locomotor re sponse to a novel environment (LR). The current experiments were desig ned to examine in more detail the behavioral differences between HR an d LR rats in non-drug paradigms. In the first experiment HR rats acqui red schedule-induced polydipsia (SIP) more readily than LR rats. Panel pressing to gain access to the food pellets, however, was greater in LR rats compared to HR rats, especially after stable levels of SIP had been attained. In the second experiment one group of rats were fed da ily after a 30-min period in photocell-cages (food conditioning; FC) w hile a control group was fed in the home-cage (non-conditioned; NC). F C subjects developed heightened locomotor activity in anticipation of feeding in the initial 30 min in the test-cage compared to NC rats. Th is anticipatory locomotor activity developed more rapidly and to a gre ater level in HR rats than in LR rats. The concentrations of dopamine, dihydroxyphenylacetic acid, homovanillic acid, serotonin, 5-hydroxyin doleactic acid, and norepinephrine were determined at the completion o f behavioral testing in both the food conditioned and non-conditioned rats. The food conditioned experiment showed that variations in both t he dopaminergic and serotoninergic systems may underlie individual dif ferences in behavioral responsiveness. However, no clear pattern of ne urochemical differences emerged. The current set of experiments have d emonstrated differences between HR and LR rats in non-drug related par adigms and that HR rats appear to show a greater motivational exciteme nt induced by periodic food delivery than LR rats.